Water generated in industrial processes and groundwater in the subsurface environment may contain various kinds of contamination, including, for example, cyanide, arsenic, chromium, selenium and halogenated organics, to name a few. Various in-situ systems for treating such contaminant-containing water using iron are known in the art. For example, U.S. Pat. No. 5,266,213 to Gillham, U.S. Pat. No. 5,362,394 to Blowes et al., and U.S. Pat. No. 5,534,154 to Gillham all disclose the use of various trench systems that include elemental iron to remove impurities from water flowing therethrough. These patents all require extremely low oxygen levels and long residences times to facilitate the removal of contaminants within the water. It is not always possible to treat contaminated water in an oxygen free environment. Moreover, long residence times restrict clean water production rates.
Various ex-situ treatment systems utilizing iron to remove contaminants from water are also known. For example, U.S. Pat. No. 5,266,213 to Gillham and U.S. Pat. No. 5,534,154 to Gillham both disclose the use of tank systems comprising elemental iron and/or activated carbon to treat contaminated water. Again, these patents both require extremely low oxygen levels within the tanks and long residence times. U.S. Pat. No. 5,837,145 to Dzombak et al. discloses the use of a fixed permeable bed of iron and sand to remove cyanide from water. These systems suffer in that, over time, iron hydroxides will precipitate into a sludge and cause clogging.
Despite these drawbacks, it is still desirable to utilize elemental iron in water treatment. Elemental iron is relatively inexpensive, widely available and is highly reactive with many of the contaminants within water. Thus, there exists a need for improved methods and systems for treating contaminated water using elemental iron.